Carts of this type already exist for transporting shopping or baggage, particularly in supermarkets, railway stations, or airports.
In outline, a cart of this type comprises a wheeled chassis, a push bar, and load-carrying means, the chassis having front and rear ends which are suitable for enabling the front end of one cart to be nested in the rear end of an identical cart which is ahead of it in a row, thereby saving space at a cart parking location in a supermarket, on a railway platform, or in an airport.
In the special case of shopping carts, the load-carrying means are constituted by a basket having a retractable wall for facilitating nesting or stacking of the carts.
Although such carts are designed to be pushed by a user pushing the push bar provided at the rear of the cart, efforts have been made over several years to motorize such carts in order to reduce the amount of force a user normally needs to exert in order to move a cart forwards, thereby making a cart more comfortable to use.
Thus, as described in U.S. Pat. No. 4,096,920, proposals have been made to fit a shopping cart with a single drive wheel and to provide a retractable trailer behind the cart serving firstly to control contact between the drive wheel and the ground and secondly to transport the user. If the user's weight is displaced towards the rear of the trailer, then the drive wheel is disengaged from the ground and a brake is caused to rub against the ground.
This prior system suffers from several drawbacks, in particular the risk of accidents due to the possibility of the user falling off the trailer. In addition, the trailer represents significant mass which is added to the mass of the cart and this makes it awkward to use the cart in the event of a breakdown.
Proposals are made in French patent number 85 13621, published under the number 2 587 291, to place a motor assembly directly between the two wheels on a single axle of a shopping cart. This assembly is essentially constituted by a motor driving a differential having outlet shafts driving the wheels directly. It is a direct drive device also including a source of energy (storage battery or solar cells), a device for controlling the speed of rotation of the motor, an electromagnetic brake, and a brake provided by the back electromotive force (emf) from the motor. This system nevertheless suffers from numerous drawbacks: the disposition of the motor between the wheels prevents carts from being nested or stacked; there is no speed reduction between the motor and the wheels which requires a motor to be used which is capable of rotating at low speed while providing high torque; no reversing facility is provided; no means are provided for automatically connecting the storage battery to a charger; and finally the use of solar cells is utterly impracticable.
More recently, in French patent application number 86 13906, published under the number 2 604 662, the present Invention has proposed a system for motorizing supermarket carts which also allows carts fitted in this way to be nested or stacked. This system includes a motor provided with a stepdown gear box and driving a differential gear whose outlet shafts are provided with wheels suitable for imparting friction drive to respective tires of two wheels of the cart. The system also provides reverse drive and means for automatically ensuring progressive starting and stopping.
This prior device also suffers from drawbacks: no means are provided for automatically recharging its battery; the friction drive gives rise to rapid wear of the drive-imparting wheels and of the tires of the driven wheels, and also to sliding of the drive wheels on the driven wheels if it is raining or a greasy or other liquid is accidentally split on the ground. In addition, this prior system is suitable for fitting to shopping carts only.
Further, in French application number 87 01046, published under the number 2 610 256, the present Invention discloses various improvements to the motorizing system of French patent application number 86 13906. In particular, means are described for automatically recharging the battery of the motorizing system.
However, this system still suffers from drawbacks in that the batteries are recharged only if the cart is properly positioned in the preceding cart of a parked row of supermarket carts or the like.
Also, the means for controlling the motorizing system are not very convenient to use, in particular since it is necessary to provide a reversing switch.
Consequently, one of the aims of the present invention is to provide a system for motorizing a shopping cart or the like which avoids the drawbacks of prior systems.
A particular aim of the invention is to provide such a motorizing system which is capable of being mounted easily on various different types of cart, including shopping carts and baggage carts.
Another aim of the invention is to provide a system which is easy for a user to use, which is rugged, and which is sufficiently compact to enable carts to be nested or stacked.
Another aim of the invention is to provide such a motorizing system which has all of the safety features desirable for the user, and which has a storage battery that is easily recharged when the cart is nested in a parked row of carts on a supermarket forecourt, or the like.